1. Field of the Invention
The invention relates to a method for regulating the electrical voltage in electrical supply networks and/or consumer units and a device for carrying out said method.
2. Discussion of Background Information
It is generally known to carry out voltage regulation only in the central network nodes of high or medium voltage networks. Further transformation to low-voltage level normally cannot be regulated under load. This network structure is oriented towards the central power supply and has the disadvantage that voltage fluctuations caused by a change in node cannot be adjusted for between the network node and the end consumer. Thus, the exploitable transfer capacity of the network components downstream from the network nodes is limited by the drop in voltage rather than by thermal strength.
Regulating transformers are provided for voltage regulation of the networks in the central network nodes. Regulating transformers are used for incremental voltage regulation in electrical networks by changing the transformer ratio. For this purpose, regulating transformers are fitted with regulating windings with tappings, which can be switched under load. During the switching processes, the load current must not be interrupted and the winding step between the relevant tappings must not be shorted. The second requirement results from the fact that during each switching process between two neighbouring tappings they are necessarily briefly connected to each other due to the first requirement, so that there is a ring current equivalent to the transformer short-circuit current between the switch and the relevant winding, the action of which the transformer is unable to withstand, especially during periodical operation. This transformer short-circuit current is relatively high, since the internal resistance of the transformer is normally small. Furthermore, the incremental switches of the transformers would have to be coordinated with the periodical switching of these high short-circuit currents.
For the above reasons, the switching process in the incremental switch of the transformer does not happen directly but rather in multiple stages, whereby transition impedances are briefly switched into the circuits of the tappings during the switching process, limiting the ring current. In Europe, ohmic transition impedances are common, and in America inductive transition impedances are common. For multi-phase switching, a number of switching principles are applied that are named after the vector diagrams of the switching processes. For example we speak of symmetrical or asymmetrical flag
The disadvantage of the measures used so far to limit the ring current is that they result in complex transition principles and require complex designs of the regulating transformers.
The aim of this invention is therefore to create a method of the type mentioned above that on the one hand avoids the above disadvantages and on the other hand allows or guarantees a better and more efficient use of the existing networks through a new field of voltage regulation application that is closer to the consumer.
The problem is solved by this invention.
The method in accordance with the invention is characterised by the fact that a regulating transformer with a transfer switch that switches the partial windings of the regulating transformer is inserted between a network node of the supply network and/or the consumer unit and at least one end consumer, whereby the regulating transformer has a high leakage impedance that limits the ring current to the order of magnitude of the nominal current in the case of a short circuit between adjacent tappings.
With this invention it is for the first time possible to carry out voltage regulation in networks or consumer units in proximity to the consumer and on the basis of regulating transformers that have an increased impedance of the regulating windings, so that a simplified step switch without transition impedances can be used.
With the liberalisation and decentralisation of electric power supply and due to the higher bi-directional work-load of the networks, the voltage differences between heavy-duty consumption, low duty and possibly the power supply will become greater on the consumer side. To maintain the voltage there should therefore be voltage regulation at the level of the low voltage or possibly at the level of the medium voltage as an economic solution.
It is a further aim of the invention to provide a device for carrying out this method, which has a simple and robust structure and which can be manufactured economically.
According to a special feature of the invention, the device for carrying out the method is characterised by the fact that the regulating transformer is designed as a longitudinal regulator with a differential capacity that is proportional to the voltage difference that is to be regulated. In accordance with the invention, longitudinal regulators for voltage maintenance are therefore provided in the network spurs, which do without the known and currently common transition impedances of the step switch and thus the resistance contacts. This is primarily possible because the voltage regulation is carried out at low-duty network points. Even an increased impedance of such a longitudinal regulator will only have a marginal effect on the total internal resistance of the network.
The need for transition impedances results from the fact that for reasons of voltage maintenance the internal network resistance and short-circuit impedance of regulating transformers is much lower than the load impedance, so that the short-circuit currents are significantly higher than the operating currents.
If the short-circuit impedance of the regulator winding is increased, e.g. by widening the leakage gap, so that the ring circuit in the case of a short circuit between adjacent tappings is of the order of magnitude of the nominal current, the additional transition impedances are not required and the step switch is simplified into a normal transfer switch.
The regulating winding can be designed both as a concentric winding and as a flat coil winding with the relevant tappings. This principle can be applied both to full transformers with regulating winding and to one-coil transformers for longitudinal regulation. The regulating winding can be connected to the secondary winding or primary winding both via one end of the winding and via a tapping.
Since the device is suitable for the voltage regulation of network spurs, its capacity based on the transitional capacity lies within a range of a some 10 kVA to some 10 MVA.
In a further embodiment of the invention, the transfer switch is a load switch without resistance contact and with only main contacts. As already shown above, such a load transfer switch offers an economical solution.
In a further embodiment of the invention, the transfer switch is a load selector without resistance contacts. This embodiment of the transfer switch also has an extremely simple structure and can be produced economically.
In further embodiments of the invention, the transfer switch can also be designed on the basis of a multi-phase camshaft controller or a chain of relays or contactors or a chain of electronic switches, in particular semiconductor switches. These embodiments of the transfer switch also have a simple structure and are extremely reliable in robust operations.
The present invention is directed to a method to regulate electric voltage in at least one of electric supply networks and consumer units with a regulating transformer located between a network node of the at least one of the electric supply networks and the consumer units and at least one end consumer, in which the regulating transformer has switchable partial windings. The process includes switching the partial windings of the regulating transformer with a transfer switch. In this manner, in an event of a short circuit between adjacent tappings of the partial windings, the regulating transformer has a high leakage impedance that limits ring current to an order of magnitude of a nominal current.
The present invention is directed to an apparatus arranged to perform a the above-noted method.
According to the invention, the transfer switch can include a load switch without resistance contacts. Further, the load switch may include only main contacts.
In accordance with an other feature of the invention, the transfer switch may include a load selector, and the load selector can be arranged without resistance contacts.
Further, according to features present invention, the transfer switch may include a multi-phase camshaft controller.
According to still another feature of the instant invention, the transfer switch can include a chain of one of relays and contactors.
In accordance with yet another feature of the invention, the transfer switch may include a chain of electronic switches. The chain of electronic switches may include semiconductor switches.
The present invention is directed to an apparatus to regulate electric voltage in at least one of electric supply networks and consumer units that includes a regulating transformer, positioned between a network node of the at least one of the electric supply networks and the consumer units and at least one end consumer, that includes a plurality of switchable partial windings, and a transfer switch arranged to selectively contact tappings of the switchable partial windings. The regulating transformer includes a leakage gap such that, in the event of a short circuit between adjacent tappings of the switchable partial windings, the regulating transformer has a high leakage impedance that limits ring current to an order of magnitude of a nominal current.